Fire detector

ABSTRACT

The fire detector comprises an insertable detector assembly which includes a sensor arrangement ( 2 ), an electronic evaluation system and a housing ( 3 ) which surrounds the sensor arrangement ( 2 ) and has openings to provide access by air and, when applicable, smoke to the sensor arrangement ( 2 ). The detector is of modular construction and is configured to accommodate detection modules having sensors for different fire parameters, all detection modules being compatible with a single housing ( 3 ). The detection module may be configured for optical, thermal or optical-thermal fire detection and/or for detecting combustion gases.  
     The sensor arrangement ( 2 ) and the above-mentioned access openings are arranged substantially in one plane, whereby a shallow construction is achieved even in the case of a multi-criterion detector. The detection modules have a carrier plate ( 6 ) which is identical for all detector types and is insertable in the detector, which carrier plate ( 6 ) is configured to accommodate the sensors for the different fire parameters

The present invention relates to a fire detector comprising aninsertable detector assembly which includes a sensor arrangement and anelectronic evaluation system, and comprising a housing which surroundsthe sensor arrangement and has openings to provide access by ambient airand, when applicable, smoke to the sensor arrangement.

The sensor arrangement may include, for example, an electro-opticalsensor for detecting scattered light generated by smoke present in theambient air, or a temperature sensor for detecting heat generated by afire, or a gas sensor for detecting combustion gases, or combinations ofthese sensors. In the fire detectors known up to now both the insertabledetector assembly and the housing are different, depending on the sensorarrangement used, so that each detector type requires its own injectionmoulding tool, thereby increasing the manufacturing cost The storage ofdifferent types of detector assemblies and housings also causes unwantedcosts.

Through the invention a standardisation of the insertable detectorassemblies and housings, and therefore a reduction in costs, are to bemade possible. The object pursued is that a single housing can be usedfor different detector types.

This object is achieved according to the invention in that the detectoris of modular construction and is configured to accommodate detectionmodules for different parameters of fire, all detection modules beingcompatible with a single housing.

The modular construction comprising one housing and different detectionmodules compatible therewith gives rise to a universally usable detectorwith a standardised external appearance. This has an aestheticallypleasing effect and also brings about an appreciable reduction inmanufacturing costs.

So-called optical-thermal detectors which include an electro-opticalsensor and a temperature sensor are in widespread use today. In thesedetectors the temperature sensor is in most cases arranged at a levelbelow the electro-optical sensor, preferably on the centre axis of thedetector. The above-mentioned access openings are also usually locatedat this lower level. This gives rise to a “multistorey” structure of thedetector which determines its height. In many cases, however, the lowestpossible height of the detector is desired for aesthetic reasons.

A further object of the invention is to specify a fire detector having ahousing which is compatible with the different detection modules and isof the lowest possible height.

This object is achieved according to the invention in that the sensorarrangement and the above-mentioned access openings are arrangedsubstantially on one level.

The detector according to the invention is therefore a relativelyshallow detector which can be used both as a multi-criterion detectorand as a single-criterion detector. The low height of the detector ismade possible by the arrangement of the sensor arrangement and theaccess openings on one level.

A first preferred embodiment of the fire detector according to theinvention is characterised in that the detection modules have a carrierplate which is usable for all detector types, is insertable in thedetector and is configured to receive the sensors for the different fireparameters.

A second preferred embodiment is characterised in that the carrier platehas on its underside facing towards the detector cap housings forreceiving components of an electro-optical sensor system and isconfigured on its upper side for mounting a printed circuit boardcarrying the electronic evaluation system.

A third preferred embodiment of the fire detector according to theinvention is characterised in that the housing includes a detector hoodconsisting of an annular upper part and a lower part spaced therefromand forming the cap of the detector. The gap between the two parts ofthe detector hood forms the above-mentioned access openings and theabove-mentioned lower part is connected to the upper part by arcuate orrib-like bridges.

A fourth preferred embodiment is characterised in that there is providedan optical detection module for measuring scattered light caused bysmoke, which optical detection module comprises at least one lightsource, a light detector, a measuring chamber and a labyrinth systemhaving screens arranged at the periphery of the measuring chamber, theat least one light source and the light detector being fixed in thehousings on the underside of the carrier plate and the labyrinth systembeing configured in the manner of a cover and being fixable to thecarrier plate.

A further preferred embodiment is characterised in that there isprovided a thermal detector module having two temperature sensors whichare fixed to the printed circuit board in radially opposed locations andproject downwardly therefrom through the carrier plate. A furtherdevelopment of this embodiment is characterised in that theabove-mentioned bridges are configured in the form of wings or straps,each having a vertically disposed opening, and are provided in an evennumber, and in that the temperature sensors project from above towardsone of the bridges in each case in such a way that their free ends arelocated directly in or behind the opening. The thermal detection moduleincludes a cover plate fixable to the carrier plate for covering thehousing provided for the electro-optical sensor system, and there areprovided in the cover plate openings through which the temperaturesensors can pass and a dividing wall disposed radially between thetemperature sensors for effecting a directed air-flow.

A further preferred embodiment of the fire detector according to theinvention is characterised in that there is provided an optical-thermaldetection module for measuring scattered light caused by smoke and formeasuring temperature, which detection module includes anelectro-optical sensor system and two temperature sensors, the latterbeing arranged laterally beside the optical sensor system.

According to a further development of this preferred embodiment thetemperature sensors are fixed to the printed circuit board in radiallyopposed locations and their free ends are located in each case in thevicinity of one of the above-mentioned bridges. The bridges arepreferably so configured that, firstly, they protect the temperaturesensors from mechanical influences and, secondly, they ensure air-flowto the temperature sensors which is as undisturbed as possible.

The invention is elucidated in detail below with reference to exemplaryembodiments and to the drawings, in which:

FIG. 1 is a perspective view of a first embodiment of a detectoraccording to the invention seen from the front and below;

FIG. 2 is a perspective view of a cross-section through the detector ofFIG. 1;

FIG. 3 is a perspective view of an axial section through the detector ofFIG. 1;

FIG. 4 is a plan view of the detector of FIG. 1;

FIG. 5 is a perspective representation of a top view of the detector ofFIG. 1 without base but with base terminal:

FIG. 6 is a perspective view of a second embodiment of a detectoraccording to the invention seen from the front and below;

FIG. 7 is a perspective view of the detector of FIG. 6 with the detectorcap removed, seen from below, and

FIG. 8 is a perspective view of an axial section through the detector ofFIG. 6.

The smoke detector illustrated in FIGS. 1 to 5 comprises in knownfashion three main components, a base 1, an optical sensor system 2 anda housing 3. This structure is most clearly seen in FIG. 3. FIG. 2 showsa view of a part of the optical sensor system 2 viewed from below in across-section through the detector.

The base 1 is provided for mounting to the ceiling of the room to bemonitored, mounting being effected either directly to a flush box or toa surface socket with or without additional plinth. The base 1, whichconsists essentially of a circular plate and a downwardly projectingperipheral flange, contains among other elements a multi-pole connector4 (FIGS. 3, 4) which is provided to receive a multiple plug 5 (FIG. 5)connected to the sensor system.

The optical sensor system 2 contains a plate-like carrier 6 for theoptical sensor, a cover-like labyrinth 7 fixed to the underside of thecarrier 6, a printed circuit board 8 arranged on the upper side of thecarrier 6 facing towards the base 1 and having the electronic evaluationsystem, and a cover 9 which closes the printed circuit board 8peripherally and upwardly and which forms part of the housing 3. Themultiple plug 5 is an integrated component of the carrier plate 6 andprojects upwardly therefrom. The cover 9 has substantially the form of aplate having a flange around its periphery and having an opening 10through which the multiple plug 5 can pass so that the latter projectsinto the plane of the multi-pole connector 4 arranged in the base 1.

The optical sensor which can be seen in FIG. 2 contains a measuringchamber formed by the carrier 6 and the labyrinth 7, and having a lightdetector 11 and two light sources 12, 12′ arranged in housings 13, 14,15 respectively. These housings consist of a base part in which therespective diode (photodiode or IRED) is mounted and which has on itsfront side facing towards the centre of the measuring chamber a windowopening for the ingress and egress of light. As is apparent from theFigure, the scatter chamber formed in the measuring chamber in thevicinity of the above-mentioned window-like openings in the housings 13,14, 15 is compact and open. This arrangement and configuration make thedetector optimally suited to the use of a transparent body insertableinto this scatter chamber for smoke simulation. Such transparent bodiesare used for calibrating or testing smoke-sensitivity during manufactureof the detectors (cf. EP-B-0 658 264).

The frames of the window openings are formed in one piece, at least forthe housings 14 and 15, whereby the tolerances for smoke-sensitivity arereduced. In known scattered-light smoke detectors the window framesconsist of two parts, one of which is integrated with the cover and theother with the base of the measuring chamber. When fitting the base,difficulties of fit constantly occur, giving rise to variable windowsizes and to the formation of a light gap between the two halves of thewindow, and therefore to unwanted disturbances of the transmitted anddetected light. With the one-piece housing windows disturbances of thiskind are precluded and no problems with the positioning accuracy of thewindow halves can arise The windows are rectangular or square and thereis a relatively large distance between the respective window openingsand the associated light sources 12, 12′ and the lens of the associatedlight detector 11, whereby a relatively small aperture angle of thelight rays concerned is produced. A small aperture angle of the lightrays has the advantage that, firstly, almost no light from the lightsources 12, 12′ impinges on the base and, secondly, the light detector11 does not “see” the base, so that dust particles deposited on the basecannot generate any unwanted scattered light. A further advantage of thelarge distance between the respective windows and the light sources 12,12′ and the lens of the light detector 1 1 is that the optical surfacespenetrated by light are located relatively deeply inside the housingsand therefore are well protected from contamination, resulting inconstant sensitivity of the optoelectronic elements.

The labyrinth 7 consists of a floor and peripherally arranged screens 16and contains flat covers for the above-mentioned housings 13, 14. 15.The floor and the screens 16 serve to shield the measuring chamber fromextraneous light from outside and to suppress so-called background light(cf. EP-A-0 821 330 and EP-A-1 087 352). The peripherally arrangedscreens 16 consist in each case of two sections forming anL-configuration. Through the shape and arrangement of the screens 16,and in particular through their reciprocal distances, it is ensured thatthe measuring chamber is sufficiently screened from extraneous lightwhile its operation can nevertheless be tested with an optical test set(EP-B-0 636 266). Moreover, the screens 16 are arranged asymmetricallyso that smoke can enter the measuring chamber similarly well from alldirections.

The front edge of the screens 16 oriented towards the measuring chamberis configured to be as sharp as possible so that only a small amount oflight can impinge on such an edge and be reflected The floor andcovering of the measuring chamber, i.e. the opposed faces of carrier 6and labyrinth 7, have a corrugated configuration, and all surfaces inthe measuring chamber, in particular the screens 16 and theabove-mentioned corrugated surfaces, are glossy and act as blackmirrors. This has the advantage that impinging light is not scattereddiffusely but is reflected in a directed manner.

The arrangement of the two light sources 12, and 12′ is selected suchthat the optical axis of the light detector 11 includes an obtuse anglewith the optical axis of the one light source, light source 12 accordingto the drawing, and an acute angle with the optical axis of the otherlight source, light source 12′ according to the drawing. The light oflight sources 12, 12′ is scattered by smoke which penetrates themeasuring chamber and a art of this scattered light impinges on thelight detector 11, being said to be forward-scattered in the case of anobtuse angle between the optical axes of light source and light detectorand being said to be backscattered in the case of an acute angle betweensaid optical axes.

It is known that the scattered light generated by forward-scattering issignificantly greater than that generated by backscattering, the twocomponents of scattered light differing in a characteristic manner fordifferent types of fire. This phenomenon is known, for example, fromWO-A-84/01950 (=U.S. Pat. No. 4,642,471), which discloses, among othermatters, that the ratio of scatter having a small scattering angle toscatter having a larger scattering angle, which ratio differs fordifferent types of smoke, can be utilised to identify the type of smoke.According to this document, the larger scattering angle may be selectedabove 90°, so that the forward-scattering and backscattering areevaluated. The evaluation of the scattered light components originatingfrom the two light sources 12 and 12′ is not the subject of the presentApplication and is therefore not described in detail here

For better discrimination between different aerosols, active or passivepolarisation filters may be provided in the beam path on the transmitterand/or detector side The carrier 6 is suitably prepared and grooves (notshown) in which polarisation filters can be fixed are provided in thehousings 13, 14 and 15. As a further option, diodes which transmit aradiation in the wavelength range of visible light (cf. EP-A-0 926 646)may be used as light sources 12, 12′, or the light sources may transmitradiation of different wavelengths, for example, one light sourcetransmitting red light and the other blue light.

The housing 3 of the smoke detector is constructed essentially in twoparts and consists of the above-mentioned cover 9 and a detector hood 17surrounding the optical sensor system 2. Said hood 17 consists of anupper annular part and a plate spaced therefrom which forms the cap ofthe detector and is connected to the upper annular part by arcuate orrib-like bridges 18. The gap, designated by reference numeral 19,between the upper and lower parts of the detector hood 17 forms anopening disposed around the full circumference of the housing to provideaccess by air and therefore smoke to the optical sensor system 2, thisopening being interrupted only by the relatively narrow bridges 18. Aneven number of bridges 18 are provided, there being four according tothe drawings. The detector hood 17 and the cover 9 are fixed to thesupport 6 by means of hook-like snap connections (not shown) and thewhole detector is fixed in the base 1. Recessed in the upper part of thedetector hood 17 is a ring 20 which carries an insect mesh 21 made of asuitable flexible material. As the detector hood 17 is fitted thecarrier 6 is pressed against the ring 20, whereby the insect mesh 21 isfixed in the detector. The detector is fixed to the base 1 by means of akind of bayonet connection. The detector is pushed into the base 1 frombelow, which is possible in only a single relative position betweendetector and base because of a mechanical coding formed by guide ribsand guide grooves. The detector is then rotated in the base 1 through anangle of approximately 20° (FIG. 4), whereby the multiple plug 5 formingpart of the carrier 6 and projecting upwardly therefrom is insertedtangentially into the multi-pole connector mounted in the base 1 andelectrical contact between the multi-pole connector 4 and the multipleplug 5, and therefore between detector and base, is established. Thedetector is then mechanically fixed into the base 1 by means of theabove-mentioned bayonet connection. The multiple plug 5 is integratedwith the upper face of the carrier 6 and manufactured in one piece withthe carrier 6 using so-called insert technology. The electricalconnections are taken from the plug contacts of the multiple plug 5 to astamped part moulded into the carrier 6 by means of metal conductorsinsulated from one another The free ends of these metal conductorsproject from the carrier 6 beside the multiple plug 5 and form contactpoints for producing soldered connections to the electronic evaluationsystem on the printed circuit board 8.

The electrical connection between detector and base by means of the twoelements: multi-pole connector 4 and multiple plug 5, has a number ofadvantages:

-   -   a simple mechanical action is required to establish the plug        connection and, in particular, no conversion of a rotary into a        translational motion is required;    -   the compact plug connection permits the use of simple loop        contacts and possesses excellent characteristics with regard to        electromagnetic compatibility (EMC).

As is apparent from FIG. 3, a light guide 22 is fixed to the componentforming the floor of the labyrinth 7, one end of which light guide 22projects upwardly to the printed circuit board 8 while its other endprojects from the detector hood 17 through a hole in the lower part ofthe detector hood. In the region of said hole the detector hood isprovided with a spherical recess 23 which surrounds the free end of thelight guide 22. The light guide 22 therefore serves as an alarmindicator for optical display of alarm states of the detector.

For this purpose an LED (not shown) which is activated in an alarm stateand supplies light to the light guide 22 is provided on the printedcircuit board 8.

If a detector executes an alarm signal, as a rule a visual check is madeto determine whether the alarm indicator is actually displaying analarm. It is evident that the alarm indicator must be visible from allsides in order to make this check. Where this is not the case thedetectors must be mounted in the room monitored in such a way that thealarm indicator is clearly visible from the doorway. In the case ofpurely thermal detectors in which, because of the absence of an opticalsensor, there are no restrictions on the arrangement of the alarmindicator, the latter is often arranged at the apex of the detector (cf.U.S. Pat. No. 5,450,066). In the case of scattered-light smoke detectorsthis is possible only with restrictions because, firstly, a light guidemounted on the axis of the detector, and therefore passing through thescatter chamber, is out of the question, so that a curved light guidewould have to be used and, secondly, the electrical connection to an LEDmounted at the apex of the detector would be too complex and costly. Forthis reason, in the case of scattered-light smoke detectors, the alarmindicator is as a rule arranged at the periphery of the detector (cf.DE-A-100 54 111) and in practice is visible from only a very small solidangle, giving rise to the above-mentioned problems with regard tomounting and positioning the detectors Proposals regarding all-roundvisibility of the alarm indicator of scattered-light smoke detectorstend in the direction of annular or strip-like light guides around theentire periphery of the detector hood (EP-1 049 061). However, thesesolutions are not satisfactory because a light guide with such a largeluminous surface requires a relatively large amount of current in orderto shine brightly enough to ensure reliable detection of alarm displays.

The alarm indicator requires only a small amount of current and, becauseit is located in the region of the apex of the detector, is visiblepractically on all sides. It is true that all-round visibility existsonly from a viewing angle of 20° to the horizontal, but because thedetector is mounted to the ceiling this condition is fulfilled in mostcases. As can be seen in particular in FIG. 2, the light guide 22 passesthrough the measuring chamber in the area between the housings 14 and15. The two housings 14 and 15 are connected together by their frontfaces and therefore form, with their inner side faces and the connectingface between the latter, a wall surrounding the light guide 22 whichlargely screens the scatter chamber of the measuring chamber from thelight guide 22.

The smoke detector described heretofore is a purely optical detectorwith smoke detection making use of the scattered light caused by smokeparticles which have penetrated the measuring chamber. The detector mayoptionally be configured as a dual-criterion detector and additionallyinclude a temperature sensor. According to FIGS. 1 and 2, twotemperature sensors 24 formed by NTC resistors are provided which arearranged in the vicinity of two bridges 18 located opposite one another.The bridges 18 have at their centre an elongated aperture 25 into whichthe temperature sensors 24, which are mounted on the printed circuitboard 8, project from above. Optical-thermal detectors are known, sothat a description of the signal evaluation process may be omitted here.The detector could, of course, include still further sensors, forexample, a combustion gas sensor (CO, NO_(x)), which, if ofappropriately small dimensions, could be arranged inside the measuringchamber.

Whereas temperature sensors arranged on the axis of the detector arecompletely independent of direction, in the case of a peripherallyarranged sensor directional dependence is high and response behaviourdepends on whether the sensor is located on the side of the detectorfacing towards or away from the fire. This problem is solved by the useof two temperature sensors 24 located opposite one another. Furtherdetails on these sensors are to be found in the description of FIGS. 6to 8. What is essential is that the sensor has homogeneous, rotationallysymmetrical sensitivity regardless of the incoming flow direction. Thisis achieved by the bridges 18 in cooperation with the labyrinth 7, thebridges 18 on the one hand protecting the temperature sensors 24 againstthe effects of mechanical forces and conducting the air optimally to thesensors and, on the other, guiding the air along the outside of thehousing in cooperation with the labyrinth 7.

As already mentioned in the introduction to the description, optical,optical-thermal and thermal fire detectors are in use today, to whichgas detectors may also be added. Moreover, the optical, thermal andoptical-thermal detectors may additionally include a combustion gassensor. The detector illustrated in FIGS. 1 to 5 represents the opticaland optical-thermal variants (supplemented by the combustion gas sensor,if applicable), no temperature sensors 24 being present, of course, inthe case of the purely optical detector. Apart from these differences,the mechanical construction of the detectors in the two variantsdescribed heretofore is identical.

As will now be elucidated with reference to FIGS. 6 to 8, without designchanges to the base or housing the detector may also be used as thebasis for a purely thermal detector. Because the main mechanicalcomponents and the structure of the detector are therefore always thesame in all cases, there is proposed a family of fire detectors havingsensors for different fire parameters for which a single housingidentical in all cases and a single base are sufficient, wherebysubstantial savings are made possible.

The thermal fire detector represented in FIGS. 6 to 8 differs from theoptical-thermal detector represented in FIGS. 1 to 5 essentially by thefollowing features:

-   -   the light sources 12 and 12′ and the light detector 11 are        omitted;    -   the ring 20 and the mesh 21 are omitted;    -   the labyrinth 7 is omitted and replaced by a cover plate 26.

The cover plate 26 is a very fundamental part of the thermal firedetector because it makes possible, among other features, for one andthe same carrier 6 to be used for the different types of detector. Ascan be seen in particular in FIG. 7, which shows a view of the coverplate 26 from below, the latter includes openings adapted to thecontours of the housings 13, 14 and 15, through which the lower ends ofthe above-mentioned housings project. In addition, elastic tongues 27,28 and 29 are provided on the cover plate 26, which serve to cover thehousings 13, 14, 15 and are snapped into same. Furthermore, the coverplate 26 includes a tubular mounting 30 for the light guide 22, twoopenings for the temperature sensors 24 and a dividing wall 31, which isdisposed between the latter and serves to effect a directed air flow.

The dividing wall 31 contributes substantially to enabling theabove-described thermal fire detector to have homogeneous sensitivityand to meet the strict requirements of standard EN 54/5, Class A1.Together with the bridges 18, the dividing wall 31 guides the inflowingair through the housing to the sensors 24.

In evaluating the signals of the two temperature sensors 24, either thehigher value or the mean value may be taken into account, or the twovalues may be weighted and used jointly for evaluation. The responsebehaviour of the temperature sensors gives an indication of the locationof the fire, since it can be assumed that the fire is located on theside of the detector having the sensor which supplies the highertemperature value.

A further advantage of the use of two temperature sensors 24 is theredundancy associated therewith. The two sensors monitor one another,and drift or ageing is detectable considerably earlier than in the caseof a single sensor. The monitoring of the two sensors over a relativelylong period must yield approximately the same temperature for both. Ifthis is not the case, a malfunction is present in one of the sensors.

In the case of the optical-thermal detector illustrated in FIGS. 1 to 5,optimum redundancy (two light transmitters, two light detectors, twotemperature sensors) can be achieved by using a double photodiode as thelight detector 11.

FIGS. 1 to 8 do not illustrate a single detector but a detector systemwhich is characterised by three main features:

-   -   all detectors have the same appearance, at least when viewed        from the usual distance of more than 2 m;    -   the detectors are shallow and “single-storey”;    -   the detectors are of modular construction and therefore are        cost-effective to manufacture.

Each detector of the system, whether a single-criterion or amulti-criterion detector and whether optical or thermal, has the samebase 1, the same housing 3 and the same carrier 6. The individualdetectors differ only in the detection module, i.e. the particularsensor arrangement used. The detection module for an optical detectorconsists of the carrier 6, the optoelectronic elements 11, 12, 12′, thelabyrinth 7 and the mesh 21 with the ring 20; the detection module for athermal detector consists of the carrier 6, the thermal sensors 24 andthe cover plate 26, and the detection module for an optical-thermaldetector consists of the carrier 6, the optoelectronic elements 11, 12,12′, the labyrinth 7, the mesh 21 with the ring 20 and the thermalsensors 24, the printed circuit board 8 being, of course, specific tothe type of detector.

A detector module for a gas detector is also possible as an additionaldetection module, the sensor concerned also being mounted, wherepossible, on the carrier. A different possibility consists in arrangingthe gas sensor laterally beside the fire detector or in a separatehousing offset from the detector and preferably arranged laterallybeside same or moulded therewith. Possibilities for further modules are,for example, a module for measuring radiation power, a camera or analarm module with an acoustic alarm emitter (cf. EP 01 128 683.8).

1. A fire detector, comprising an insertable detector assembly whichincludes a sensor arrangement and an electronic evaluation system, and ahousing which surrounds the sensor arrangement and has openings toprovide access by air and, when applicable, smoke to the sensorarrangement, wherein the detector is of modular construction and isconfigured to accommodate detector modules having sensors for differentfire parameters, all detection modules being compatible with a singlehousing.
 2. The fire detector of claim 1, wherein the sensor arrangementand the access openings are arranged substantially in one plane.
 3. Thefire detector of claim 2, wherein the detection modules have anidentical carrier plate for all detector types, which carrier plate isinsertable in the detector and is configured to accommodate the sensorsfor the different fire parameters.
 4. The fire detector of claim 3,wherein the carrier plate includes, on its underside facing towards adetector cap, housings for accommodating components of anelectro-optical sensor system and is configured on its upper side formounting a printed circuit board carrying the electronic evaluationsystem.
 5. The fire detector of claim 4, wherein the housing includes adetector hood comprising an annular upper part and a lower part spacedtherefrom and forming the cap of the detector.
 6. The fire detector ofclaim 5, wherein a gap between the two parts of the detector hood formsthe access openings and the lower part is connected to the upper part bybridges.
 7. The fire detector of claim 4, and further comprising anoptical detection module for measuring scattered light caused by smokeincluding at least one light source, a light detector, a measuringchamber and a labyrinth system having screens arranged at its periphery,the at least one light source and the light detector being fixed in thehousings on the underside of the carrier plate and the labyrinth systembeing formed in the manner of a cover and being fixable to the carrierplate.
 8. The fire detector of claim 6, further comprising a thermaldetection module having two temperature sensors which are fixed to theprinted circuit board radially opposite one another and projectdownwardly from the latter through the carrier plate.
 9. The firedetector of claim 8, wherein the bridges are configured in the form ofwings or straps having a vertically disposed opening and are provided inan even number, and in that the temperature sensors project from abovetowards one of the bridges in each case in such a way that their freeends are located directly in or behind the opening.
 10. The firedetector of claim 9, wherein the thermal detection module has a coverplate fixable to the carrier plate for covering the housings which areprovided for the electro-optical sensor system, and in that openingsthrough which the temperature sensors can pass are provided in the coverplate and a dividing wall for effecting a directed air-flow is providedbetween the temperature sensors and is disposed in a radial direction.11. The fire detector of claim 6, further comprising an optical-thermaldetection module for measuring scattered light caused by smoke and formeasuring temperature, which detection module includes theelectro-optical sensor system and two temperature sensors, the latterbeing arranged laterally beside the optical sensor system.
 12. The firedetector of claim 1, wherein the temperature sensors are fixed to theprinted circuit board radially opposite one another and their free endsare located in the vicinity of the bridges.
 13. The fire detector ofclaim 12, wherein the bridges are so configured that they protect thetemperature sensors from mechanical influences and ensure air-flow tothe temperature sensors which is substantially as undisturbed.
 14. Thefire detector of claim 7, further comprising a light guide is fixed tothe base of the labyrinth system, which light guide extends upwardly tothe printed circuit board and forms part of an alarm display visible inthe region of the apex of the detector.
 15. The fire detector of claim14, further comprising a base associated with the housing of the firedetector and having a multi-pole connector, and by a multiple plugarranged in the housing of the fire detector and insertable tangentiallyin the multi-pole connector by rotating the housing of the detectorrelatively to the base.
 16. The fire detector of claim 15, wherein themultiple plug is integrated in the carrier plate using inserttechnology.
 17. The fire detector of claim 16, further comprising analarm module having an acoustic alarm emitter arranged in a separatehousing offset from the housing of the fire detector.
 18. The firedetector of claim 9, wherein the bridges are so configured that theyprotect the temperature sensors from mechanical influences and ensureair-flow to the temperature sensors which is substantially undisturbed.19. The fire detector of claim 1, further comprising an alarm modulehaving an acoustic alarm emitter arranged in a separate housing offsetfrom the housing of the fire detector.
 20. The fire detector of claim 6,further comprising an alarm module having an acoustic alarm emitterarranged in a separate housing offset from the housing of the firedetector.